A test device considering wind-wave coupling and floating wind turbine vibration

Abstract

The present invention discloses a test device that takes into account wind-wave coupling and floating wind turbine vibration, belonging to the field of wind tunnel test technology. The test device comprises a base, a connecting rod, a tension spring, a connecting pipe, a circular ring, an arc block, a floating wind turbine model, a slider and a movable rod. By controlling two sliders located in the same straight line to alternately drive the floating wind turbine model to swing back and forth, the floating wind turbine model can be simulated to swing under the influence of waves in a real ocean environment. At the same time, in conjunction with the different wind speeds blown out by the wind tunnel, the wind is fluid-solid coupled with the wind turbine blades in different changing positions, and parameters such as the aerodynamic loads on the blades at different angles can be tested, which is helpful for improving the aerodynamic shape of the blades.

Description

Technical Field

[0001] The invention belongs to the technical field of wind tunnel testing, and in particular relates to a testing device taking into account wind-wave coupling and floating wind turbine vibration. Background Art

[0002] A floating wind turbine is a wind turbine that floats on the sea. To measure parameters such as the aerodynamic loads acting on the tower and blades of the floating wind turbine, and to consider fluid-solid coupling and facilitate the optimization of the blade aerodynamic shape in the later stage, it is necessary to conduct simulation tests on the corresponding floating wind turbine model so that the manufactured real floating wind turbine can be put into use directly. Therefore, a test device is needed to simulate the real sea surface working environment of the floating wind turbine. CN110501139B discloses a wave simulation device and method. Although this device can simulate waves, it does not fit well with the floating wind turbine model. When tested in a wind tunnel, the wind-wave coupling conditions in the real ocean environment are not met, making the tested aerodynamic loads and other parameters have no reference significance and are of no help in improving the aerodynamic shape of the blades. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a test device that takes into account wind-wave coupling and floating wind turbine vibration, so as to solve the technical problem that the wave simulation device in the prior art cannot fit well with the floating wind turbine model, and when conducting tests in a wind tunnel, it does not meet the wind-wave coupling conditions in the real ocean environment, making the tested aerodynamic load and other parameters have no reference significance and are of no help to the improvement of the aerodynamic shape of the blade.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] The present invention provides a test device taking into account wind-wave coupling and floating wind turbine vibration, comprising a base and a connecting rod with a ball joint on the base; a plurality of tension springs connected to the base are evenly arranged on the circumferential side of the connecting rod; a connecting tube with one end closed is provided at the end of the connecting rod away from the base through a first spring sliding sleeve; a circular ring is provided on the circumferential side of the connecting tube away from the closed end; a first annular groove is coaxially opened on the circumferential side of the circular ring; a plurality of arc blocks are slidably connected in the first annular groove; the closed end of the connecting tube is used to connect a floating wind turbine model; an annular track is coaxially provided on the base and located outside the connecting rod; a plurality of sliding rails arranged radially along the connecting rod are slidably connected on the annular track; a slider corresponding to the arc block is slidably connected on each sliding rail; a movable rod is ball-jointed on the arc side wall of the arc block; a movable groove is opened at the free end of the movable rod; a first cylinder is rotatably connected between the opposite side walls of the movable groove through a rotating shaft arranged perpendicular to the connecting rod; the first cylinder is arranged perpendicular to the rotating shaft, and the telescopic end of the first cylinder is ball-hinged on the slider.

[0006] Furthermore, each arc block is provided with an arc groove running through the side wall away from the base; a plurality of splicing blocks connected in sequence are provided in the arc groove along the radial direction of the arc block; a fixed groove is coaxially provided on the side of each splicing block away from the base in the same direction as the arc groove; a rotating ring is provided on the connecting pipe for coaxial rotation; a second cylinder is connected to the second cylinder along the radial direction on the circumference of the rotating ring; a wire tube is connected to the telescopic shaft of the second cylinder; a through hole is provided on the circumference of the wire tube near one end; the other end of the wire tube is connected to the central An empty accommodating cylinder; a winding ring is rotatably connected inside the accommodating cylinder; a steel wire is passed through the wire tube; one end of the steel wire is wound with the winding ring; the other end of the steel wire passes through the through hole and an end head is exposed outside; a movable part that can clamp the end head and clamp the steel wire is provided in the fixed groove; the rotation of the rotating ring causes the steel wire to leak out of the through hole and be spirally wound around the fixed groove of each splicing block from the inside to the outside, forming a plurality of arc-shaped strings separated by the splicing blocks; the rotating ring is provided with a plucking unit that can pluck the arc-shaped strings.

[0007] Furthermore, the base is provided with a plurality of arc baffles which are sequentially located on the outside of the circular track; each arc baffle is coaxially connected to the base; each arc baffle is provided with a fan-shaped groove which passes through the inner and outer circumferences; the fan-shaped groove is rotatably connected with an expansion axis between opposite side walls perpendicular to the base; a fan-shaped guide plate is rotatably connected in the fan-shaped groove through the expansion axis; the inner circumference of the fan-shaped guide plate is provided with a plurality of guide units in a rectangular array; each guide unit includes a guide groove provided along the axial direction of the arc baffle; a guide block is slidably connected in the guide groove; an elliptical block is rotatably connected to the guide block.

[0008] Furthermore, the toggle unit includes a second annular groove coaxially opened on the circumferential side of the rotating ring; a third cylinder connected radially is slidably connected in the second annular groove; a vertical rod is vertically connected to the telescopic shaft of the third cylinder; a toggle groove is opened at one end of the vertical rod away from the third cylinder; a toggle rod capable of contacting the arc chord is rotatably connected between the opposite side walls of the toggle groove; the circumferential side of the toggle rod and the side wall of the toggle groove are connected by a second spring.

[0009] Furthermore, the movable part includes U-shaped blocks that are respectively connected to the side walls of the fixed groove and are arranged opposite to each other; a baffle is connected between the opposite side walls of each U-shaped block through rotation; one end of the baffle has the same magnetic poles facing each other, and the other end has the abnormal magnetic poles facing each other.

[0010] The beneficial effects of the present invention are:

[0011] 1. By controlling the two sliders located in the same straight line to alternately drive the floating wind turbine model to swing back and forth, it is possible to simulate the swaying of the floating wind turbine under the influence of waves in a real ocean environment. At the same time, combined with the different wind speeds blown out by the wind tunnel, fluid-structure coupling occurs between the wind and the wind turbine blades in different changing positions. This allows for testing parameters such as the aerodynamic loads on the blades at different angles, which helps to improve the aerodynamic shape of the blades.

[0012] 2. The floating wind turbine will swing in the waves and switch back and forth between the crests and troughs, causing the height of the floating wind turbine to change all the time. At the same time, since the wave cycle is not fixed, the switching position between the crests and troughs is different each time. The first cylinder is driven to rotate by the rotating shaft, thereby deflecting the movable rod. When the movable rod deflects, it acts on the arc block and drives the connecting pipe to slide toward the connecting rod; when the rotating shaft drives the first cylinder to rotate to the initial position, the connecting pipe returns to the initial position, thereby realizing the height change of the floating wind turbine. In conjunction with the sliding of the slider, the height position of the floating wind turbine model can be changed by controlling the rotation angle of the rotating shaft, thereby simulating the movement of the floating wind turbine under the continuously changing wave cycle, so that the test of parameters such as the aerodynamic load on the wind turbine blades is more comprehensive, which helps to improve the aerodynamic shape of the blades, so that the wind turbine blades after being put into use can adapt to the complex marine environment.

[0013] 3. Under the action of wind-wave coupling and wind turbine vibration, the aerodynamic load and other parameters of the wind turbine blades are different. By adjusting the distribution position between the arc blocks, the length of the arc chord can be adjusted, thereby controlling the frequency of vibration, thereby simulating the different vibration frequencies generated when waves of different periods hit the floating wind turbine, thereby making the collected aerodynamic load and other parameters more comprehensive, which helps to optimize the blade shape.

[0014] 4. By changing the position of the guide blocks in several guide units, the flow direction, concentration, area, etc. of the wind can be changed, thereby achieving different contact conditions with the floating wind turbine model, thereby measuring the base force and torque generated by the wind turbine model as a whole under different contact conditions. At the same time, in conjunction with the sliding slider and rotating shaft, the wind can act on the wind turbine blades from different angles and produce a fluid-solid coupling effect, thereby facilitating the improvement of the wind turbine blades.

[0015] Other advantages, objectives and features of the present invention will be described in the following description and will be apparent to those skilled in the art to some extent, or those skilled in the art can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to make the purpose, technical solutions and beneficial effects of the present invention more clear, the present invention provides the following drawings for illustration:

[0017] Figure 1 A three-dimensional diagram of the overall structure of the test device of the present invention;

[0018] Figure 2 A three-dimensional diagram of a portion of the structure of the test device of the present invention;

[0019] Figure 3A three-dimensional diagram of the connection between the ring, the movable rod and the slider of the present invention;

[0020] Figure 4 A three-dimensional diagram of the arc block of the present invention;

[0021] Figure 5 A three-dimensional diagram of the rotating ring of the present invention;

[0022] Figure 6 A three-dimensional diagram of the fan-shaped guide plate of the present invention;

[0023] Figure 7 For the present invention Figure 5 A partial enlarged view of point A in the middle;

[0024] Figure 8 A three-dimensional diagram of the puzzle piece of the present invention.

[0025] The numbers in the accompanying drawings are as follows: base 1, connecting rod 2, tension spring 3, connecting pipe 4, circular ring 5, arc block 6, floating fan model 7, annular track 8, slide rail 9, slider 10, movable rod 11, first cylinder 12, splicing block 13, fixing groove 14, rotating ring 15, second cylinder 16, wire tube 17, accommodating tube 18, end 19, arc baffle 20, fan-shaped guide plate 21, guide block 22, elliptical block 23, third cylinder 24, vertical rod 25, toggle rod 26, U-shaped block 27, and baffle 28. DETAILED DESCRIPTION

[0026] like Figures 1 to 8 As shown, the present invention provides a test device that takes into account wind-wave coupling and floating wind turbine vibration, comprising a base 1 and a connecting rod 2 with a ball joint on the base 1; a plurality of tension springs 3 connected to the base 1 are evenly arranged on the circumference of the connecting rod 2; a connecting pipe 4 with one end closed is provided at the end of the connecting rod 2 away from the base 1 through a first spring sliding sleeve; a circular ring 5 is coaxially sleeved on the circumference of the connecting pipe 4 away from the closed end; Figure 2 、 3 As shown, a first annular groove is coaxially opened on the circumference of the ring 5; a plurality of arc blocks 6 are slidably connected in the first annular groove; the closed end of the connecting pipe 4 is used to connect the floating wind turbine model 7; an annular track 8 is coaxially provided on the base 1 and is located on the outside of the connecting rod 2; a plurality of slide rails 9 arranged radially along the connecting rod 2 are slidably connected to the annular track 8; a slider 10 corresponding to the arc block 6 is slidably connected to each slide rail 9; a movable rod 11 is spherically hinged on the arc side wall of the arc block 6; a movable groove is opened at the free end of the movable rod 11; a first cylinder 12 is rotatably connected between the opposite side walls of the movable groove through a rotating shaft arranged perpendicular to the connecting rod 2; the first cylinder 12 is arranged perpendicular to the rotating shaft, and the telescopic end of the first cylinder 12 is ball-hinged on the slider 10.

[0027] The principle and beneficial effects of the above technical solution:

[0028] The test device is placed in a wind tunnel through the base 1, and the floating wind turbine model 7 is detachably mounted on the closed end of the connecting tube 4; a certain slider 10 is controlled to slide on the slide rail 9 in a direction away from the connecting rod 2, and the slider 10 drives the arc block 6 to deflect through the first cylinder 12 and the movable rod 11. Since the arc block 6 is slidably connected to the ring 5, and the ring 5 is sleeved on the connecting tube 4, when the arc block 6 is pulled, it will synchronously drive the floating wind turbine model 7 set on the connecting tube 4 to deflect. At the same time, when a certain slider 10 slides on the slide rail 9, the telescopic axis of the first cylinder 12 on the other sliders 10 is controlled to extend or shorten accordingly to adapt to the deflection of the floating wind turbine model 7, and at the same time drive the tension spring 3 to extend. When the slider 10 slides back to the initial position, the extended tension spring 3 drives the connecting rod 2 back to the initial position.

[0029] The two sliders 10 located in the same straight line alternately drive the floating wind turbine model 7 to swing back and forth, which can simulate the swinging of the floating wind turbine under the influence of waves in a real ocean environment. At the same time, combined with the different wind speeds blown out by the wind tunnel, the wind and the wind turbine blades in different changing positions undergo fluid-solid coupling, which can test parameters such as the aerodynamic loads on the blades at different angles, and help improve the aerodynamic shape of the blades.

[0030] At the same time, by changing the arc length of the slide rail 9 on the annular track 8, the distribution position of the slide rail 9 can be changed, and all the slide rails 9 can be distributed in a fan shape. From one side of the fan shape to the other side, the slider 10 in the slide rail 9 is controlled to slide and then reset, so that the floating wind turbine swings from one side to the other in a fan shape and then resets. In this process, the contact angle between the wind turbine blades and the wind changes continuously, so that parameters such as the aerodynamic load on the wind turbine blades under different situations can be tested, and then considering the impact of the complex environment in the ocean on the wind turbine blades, it is helpful to improve the aerodynamic shape of the blades.

[0031] When the floating wind turbine swings in the waves, it will switch back and forth between the crest and the trough, causing the height of the floating wind turbine to change all the time. At the same time, since the wave cycle is not fixed, the switching position between the crest and the trough is different each time. The first cylinder 12 is driven by the rotating shaft to rotate, thereby deflecting the movable rod 11. When the movable rod 11 deflects, it will act on the arc block 6 and drive the connecting pipe 4 to slide in the direction close to the connecting rod 2; when the rotating shaft drives the first cylinder 12 to rotate to the initial position, the connecting pipe 4 returns to the initial position, thereby realizing the height change of the floating wind turbine. In conjunction with the sliding of the slider 10, the height position of the floating wind turbine model 7 can be changed by controlling the rotation angle of the rotating shaft, thereby simulating the movement of the floating wind turbine under the continuously changing wave cycle, so that the test of parameters such as the aerodynamic load on the wind turbine blades is more comprehensive, which helps to improve the aerodynamic shape of the blades, so that the wind turbine blades after being put into use can adapt to the complex marine environment.

[0032] In this embodiment, Figure 4 、 5 As shown, each arc block 6 is provided with an arc groove running through both sides on the side wall away from the base 1; a plurality of splicing blocks 13 connected in sequence are provided in the arc groove along the radial direction of the arc block 6; a fixed groove 14 is coaxially provided on the side of each splicing block 13 away from the base 1 in the same direction as the arc groove; a rotating ring 15 is coaxially provided on the connecting pipe 4; a second cylinder 16 is connected to the circumference of the rotating ring 15 in the radial direction; a vertical wire tube 17 is vertically connected to the telescopic axis of the second cylinder 16; a through hole is provided on the circumference of the wire tube 17 near one end; the other end of the wire tube 17 It is connected to a hollow accommodating cylinder 18; a winding ring is rotatably connected inside the accommodating cylinder 18; a steel wire is passed through the wire tube 17; one end of the steel wire is wound with the winding ring; the other end of the steel wire passes through the through hole and an end 19 is exposed to the outside; a movable part that can clamp the end 19 and clamp the steel wire is provided in the fixed groove 14; the rotation of the rotating ring 15 causes the steel wire to leak out of the through hole and be spirally wound around the fixed groove 14 of each splicing block 13 from the inside to the outside, forming a plurality of arc strings separated by the splicing blocks 13; the rotating ring 15 is provided with a plucking unit that can pluck the arc strings.

[0033] The principle and beneficial effects of the above technical solution:

[0034] In the initial state, the wire tube 17 is located in the fixed groove 14 of a certain splicing block 13 in the innermost circle, and the movable part clamps the end 19; the rotating ring 15 rotates, and the winding ring synchronously releases the steel wire. The steel wire passes through the fixed grooves 14 of all the splicing blocks 13 in the innermost circle in turn to form the first circle of string. When it reaches the splicing block 13 that clamps the end 19, the second cylinder 16 is controlled to extend, so as to wind the second circle of steel wire, forming the second and third circles of string in turn, until all the strings are formed. Several circles of string are separated by several splicing blocks 13 to form an arc string; a plucking unit is used to pluck a certain arc string to generate vibration, and the vibration is transmitted to the splicing block 13, the arc block 6, the rotating ring 15 and the connecting pipe 4 in turn through the steel wire, and finally transmitted to the wind turbine tower model.

[0035] Under the action of wind-wave coupling and wind turbine vibration, the aerodynamic load and other parameters of the wind turbine blades are different. By adjusting the distribution position between the arc blocks 6, the length of the arc chord can be adjusted, thereby controlling the frequency of vibration, thereby simulating the different vibration frequencies generated when waves of different periods hit the floating wind turbine, thereby making the collected aerodynamic load and other parameters more comprehensive, which helps to optimize the blade shape.

[0036] In this embodiment, Figure 1 、 6As shown, the base 1 is provided with four arc baffles 20 which are sequentially located on the outside of the annular track 8; each arc baffle 20 is coaxially rotatably connected to the base 1; each arc baffle 20 is provided with a fan-shaped groove running through the inner and outer circumferences; the fan-shaped groove is rotatably connected with an expansion axis between opposite side walls perpendicular to the base 1; a fan-shaped guide plate 21 is rotatably connected in the fan-shaped groove through the expansion axis; the inner circumference of the fan-shaped guide plate 21 is in a rectangular array with a plurality of guide units; each guide unit includes a guide groove opened along the axial direction of the arc baffle 20; a guide block 22 is slidably connected in the guide groove; an elliptical block 23 is rotatably connected to the guide block 22.

[0037] The principle and beneficial effects of the above technical solution:

[0038] The four arc baffles 20 are rotated to leave an air inlet so that the air inlet is facing the floating wind turbine model 7. During the test, when the wind passes through the arc baffles 20, part of the wind enters from the air inlet, and the other part of the wind flows from the outside of the arc of the arc baffles 20. By rotating the fan-shaped guide plate 21, the size of the fan-shaped groove is changed, and this part of the wind flows along the fan-shaped guide plate 21 to the floating wind turbine model 7. By changing the position of the guide blocks 22 in the guide units, the flow direction, concentration, area, etc. of the wind are changed, thereby achieving different contact conditions with the floating wind turbine model 7, and measuring the base force and torque generated by the wind turbine model as a whole under different contact conditions. At the same time, in conjunction with the sliding slider 10 and the rotating shaft, the wind can act on the wind turbine blades from different angles and produce a fluid-solid coupling effect, thereby facilitating the improvement of the wind turbine blades.

[0039] In this embodiment, Figure 5 、 7 As shown, the toggle unit includes a second annular groove coaxially opened on the circumferential side of the rotating ring 15; a third cylinder 24 connected radially is slidably connected in the second annular groove; a vertical rod 25 is vertically connected to the telescopic axis of the third cylinder 24; a toggle groove is opened at one end of the vertical rod 25 away from the third cylinder 24; a toggle rod 26 capable of contacting the arc chord is rotatably connected between the opposite side walls of the toggle groove; the circumferential side of the toggle rod 26 and the side wall of the toggle groove are connected by two second springs.

[0040] The principle and beneficial effects of the above technical solution:

[0041] The telescopic shaft of the third cylinder 24 is controlled to extend or shorten, thereby driving the plucking rod 26 connected to the vertical rod 25 to pluck the arc string. The setting of the second spring can make the plucking rod 26 return to the initial position after plucking one steel wire, thereby facilitating the plucking of another steel wire.

[0042] In this embodiment, Figure 8As shown, the movable part includes U-shaped blocks 27 that are respectively connected to the side walls of the fixed groove 14 and are arranged opposite to each other; a blocking bar 28 is connected between the opposite side walls of each U-shaped block 27 by rotation; one end of the blocking bar 28 has the same magnetic poles facing each other, and the other end has the abnormal magnetic poles facing each other.

[0043] The principle and beneficial effects of the above technical solution:

[0044] In the initial state, one end of the two blocking bars 28 is magnetically attracted together. When the wire tube 17 passes through, the two blocking bars 28 attracted together are separated, so that the other ends of the bars 28 with the same magnetic poles facing each other are close to each other. After the wire tube 17 passes through, the other ends of the bars 28 with the same magnetic poles facing each other are close to each other, and then bounce away from each other under the action of the repulsive force, so that the ends of the bars 28 with the opposite magnetic poles with abnormal names are close to each other and clamp the steel wire.

[0045] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A test device considering wind-wave coupling and floating wind turbine vibration, characterized by: The invention comprises a base and a connecting rod with a ball joint on the base; a plurality of tension springs connected to the base are evenly arranged on the circumference of the connecting rod; a connecting tube with one end closed is provided at the end of the connecting rod away from the base through a first spring sliding sleeve; a circular ring is provided on the circumference of the connecting tube away from the closed end; a first annular groove is coaxially opened on the circumference of the circular ring; a plurality of arc blocks are slidably connected in the first annular groove; the closed end of the connecting tube is used to connect to the floating wind turbine model; an annular track is coaxially provided on the base and is located outside the connecting rod; a plurality of slide rails arranged along the radial direction of the connecting rod are slidably connected to the annular track; each slide rail is slidably connected to a plurality of slide rails arranged along the radial direction of the connecting rod The sliding block corresponds to the arc block; a movable rod is provided on the arc side wall of the arc block; a movable groove is provided at the free end of the movable rod; a first cylinder is rotatably connected between the opposite side walls of the movable groove via a rotating shaft arranged perpendicular to the connecting rod; the first cylinder is arranged perpendicular to the rotating shaft, and the telescopic end of the first cylinder is ball-hinged on the sliding block; an arc groove is provided on the side wall of each arc block away from the base and passes through both sides; a plurality of splicing blocks connected in sequence are provided in the arc groove along the radial direction of the arc block; a fixed groove is coaxially provided on the side of each splicing block away from the base in the same direction as the arc groove; a rotating ring is provided on the coaxial rotating sleeve of the connecting pipe; the rotating ring A second cylinder is connected to the circumferential side of the cylinder in a radial direction; a wire tube is connected to the telescopic shaft of the second cylinder; a through hole is opened on the circumferential side of the wire tube near one end; the other end of the wire tube is connected to a hollow accommodating cylinder; a winding ring is rotatably connected in the accommodating cylinder; a steel wire is passed through the wire tube; one end of the steel wire is wound around the winding ring; the other end of the steel wire passes through the through hole and an end head is exposed to the outside; a movable part that can clamp the end head and hold the steel wire is provided in the fixed groove; the rotation of the rotating ring causes the steel wire to leak out of the through hole and be spirally wound around the fixed groove of each splicing block from the inside to the outside, forming a plurality of arcs separated by the splicing blocks. shaped chord; a plucking unit capable of plucking the arc chord is provided on the rotating ring; a plurality of arc baffles located in sequence on the outside of the circular track are provided on the base; each arc baffle is coaxially rotatably connected to the base; each arc baffle is provided with a fan-shaped groove running through the inner and outer circumferences; the fan-shaped groove is rotatably connected with an expansion axis between opposite side walls perpendicular to the base; a fan-shaped guide plate is rotatably connected in the fan-shaped groove through the expansion axis; a plurality of guide units are provided in a rectangular array on the inner circumference of the fan-shaped guide plate; each guide unit includes a guide groove opened along the axial direction of the arc baffle; a guide block is slidably connected in the guide groove; an elliptical block is rotatably connected to the guide block.

2. The test device considering wind-wave coupling and floating wind turbine vibration according to claim 1, characterized in that: The toggle unit includes a coaxial second annular groove opened on the circumferential side of the rotating ring; a third cylinder connected radially is slidably connected in the second annular groove; a vertical rod is vertically connected to the telescopic shaft of the third cylinder; a toggle groove is opened at one end of the vertical rod away from the third cylinder; a toggle rod capable of contacting the arc chord is rotatably connected between the opposite side walls of the toggle groove; the circumferential side of the toggle rod and the side wall of the toggle groove are connected by a second spring.

3. The test device considering wind-wave coupling and floating wind turbine vibration according to claim 2, characterized in that: The movable parts include U-shaped blocks that are respectively connected to the side walls of the fixed groove and are arranged opposite to each other; a baffle is connected between the opposite side walls of each U-shaped block by rotation; one end of the baffle is provided with a magnet with the same magnetic poles facing each other, and the other end is provided with a magnet with the opposite magnetic poles facing each other.

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